Urokinase plasminogen activator receptor choreographs multiple ligand interactions: implications for tumor progression and therapy.

The urokinase plasminogen activator receptor (uPAR) has been implicated in the growth, metastasis, and angiogenesis of several solid and hemotologic malignancies. uPAR is part of a cell surface system that also consists of the serine protease uPA and several specific inhibitors (plasminogen activator inhibitors 1 and 2). This system has classically been thought to drive tumor progression by mediating directed extracellular proteolysis on the surface of migrating or invading cells, and intervening with this proteolysis by targeting uPAR has been proposed to represent a novel approach for inhibiting tumor progression. However, despite abundant evidence suggesting the utility of targeting uPAR for the treatment of cancer, there are currently no uPAR-targeted therapies being evaluated in clinical trials. Recent data have provided new insights into the role of uPAR in tumor progression. In addition to mediating proteolysis, this receptor appears to also mediate cell signaling, proliferation, and survival, and these observations have revealed novel ways to target uPAR. How these data have led to a paradigm shift in how the role of uPAR in tumor progression is perceived as well as past and present attempts to therapeutically target a molecule that is generating renewed interest as a cancer target will be discussed in this article.